1. Field of the Invention
The present invention relates to a method of plating a doctor blade. More specifically, the present invention relates to an efficient continuous plating method for doctor blades especially used for gravure (intaglio) printing, which provides the doctor blades having a coat excellent in abrasion resistance, and the present invention also relates to an apparatus therefor.
2. Description of the Related Art
In gravure (intaglio) printing, ink adhered to a non-image portion of a plate barrel is scraped away while a doctor blade is pressed against the circumferential surface of the plate barrel by a predetermined pressure. The doctor blade removes the ink on the non-image portion completely and has a function to leave a predetermined amount of ink on an image portion. Accordingly, the contact pressure between the plate barrel and the doctor blade must be always maintained at a predetermined level and a distal end portion of the doctor blade is required to have abrasion resistance.
One of methods for providing abrasion resistance to the distal end portion of the doctor blade is to form a ceramic plating layer on that portion.
This method is comprised of: adding an appropriate amount of ceramic fine powder such as silicon carbide or boron nitride to an electroless nickel bath or electric nickel bath; plating under agitation; depositing and compounding these fine powder into a plating film simultaneously with the plating; and baking the plating film as required to form a hard layer on the surface of the doctor blade.
The size of the doctor blade to be installed in a printing machine conforms to the width of a roll of the plate barrel (such as 50, 90, 120 or 400 cm). The width of the blade itself is, for example, 45, 50 or 60 mm. To carry out composite plating on these blades efficiently, a belt-like steel base material has been directly plated under a state rolled in a roll shape through a spacer (such as a steel material) that does not affect an edge portion of the blade. Thereafter, the roll of the base material has been unrolled and cut to a predetermined length to obtain a doctor blade (Japanese Patent Application Laid-open No. Hei 4-70343).
This method has the following problems:
(1) Since the spacer is used, the marks of an unplated spacer portion are left behind as a net pattern, thereby impairing the outer appearance of a product, and the product has a durability problem because the unplated portion is easy to rust;
(2) Since plating is carried out in a state that the base material is rolled, a forming effect at the time of plating remains when the base material is unrolled after plating. Therefore, a slightly curled product is obtained, a blade obtained by cutting the base material to a predetermined length has a slight warp (deformation), and contact pressure to a printing roll at both end portions is slightly different from contact pressure at a central portion. As a result, a locally abnormal weight loss is induced and printing cannot be made satisfactorily;
(3) Since the base material wound spirally is pre-treated, plated and post-treated as a set, generally, the production of doctor blade may only be made manually in the batch manner. Therefore, the mass-production of the doctor blade requires much labor. Further, an examination that secures removal of ceramic fine powder adhered to the edge of the blade and the step of polishing the edge of the blade both of which are carried out before the shipment of products must be carried out separately from a plating step; and
(4) Since not only the edge of the blade which is required functionally but also other portions of the doctor blade are uniformly plated, the consumption of an expensive chemical is large, thereby presenting a cost problem.